Engine Wall Structure and a Method of Producing an Engine Wall Structure

ABSTRACT

An engine wall structure includes an inner wall to which hot gas is admitted during engine operation, an outer wall, which is colder than the inner wall during engine operation, and at least two webs that connect the inner wall with the outer wall and delimit a cooling duct between the walls. The webs are mainly formed by a first material and the inner wall is mainly formed by a second material of other composition and other heat conductivity than the first material.

TECHNICAL FIELD

The present invention relates to an engine wall structure and to amethod of producing an engine wall structure that comprises an innerwall, to which hot gas is admitted during engine operation, an outerwall, which is colder than the inner wall during engine operation, andat least two webs that connect the inner wall with the outer wall anddelimit a cooling duct between said walls.

During engine operation, any cooling medium may flow through the ducts.However, in particular, the invention relates to engine wall structuresand a process for manufacturing engine wall structures in which there isa plurality of such webs dividing the space between the walls into aplurality of ducts, in particular for cooling the firing chamber wallsand the thrust nozzle walls of rocket engines driven with hydrogen as afuel or a hydrocarbon, i.e. kerosene, wherein the fuel is introduced inthe cold state into the wall structure, is delivered through the coolingducts while absorbing heat via the inner wall, and is subsequently usedto generate the thrust. Heat is transferred from the hot gases to theinner wall, further on to the fuel, from the fuel to the outer wall,and, finally, from the outer wall to any medium surrounding it. Heat isalso transported away by the coolant media as the coolant temperatureincreases by the cooling. The hot gases may comprise a flame generatedby combustion of gases and/or fuel.

Accordingly, the engine wall structure is preferably a thrust nozzlewall, preferably of a rocket engine.

BACKGROUND OF THE INVENTION

According to prior art, the engine wall structures of regenerativelycooled combustion chambers for liquid propellant rocket engines, coolingchannels or ducts are machined, for example by milling, in a sheet orcore that will form the inner wall, or at least part of an inner wall.In the case of regenerative cooling, this inner wall sheet may mainlycomprise copper or a copper alloy. However, other materials such assteel may also be used as the core. The resulting ducts are delimited byremaining webs, and may subsequently be filled with a filler materialsuch as a conductive resin.

Subsequently, an outer cover, defining the outer wall, is applied to andattached to the projecting webs, for example by means ofelectro-deposition. The outer wall may comprise plural layers of amaterial such as nickel or a nickel-alloy. The outer cover may,possibly, also be attached to the inside of the inner wall sheet,thereby fully surrounding the core. The filler material, transformed bymeans of heating into a liquid state, is then drained off through an endof the respective duct.

However, prior art results in an insufficient control of the exactthickness of the remaining inner wall, due to the inherent problem ofobtaining an exact milling depth in the inner wall sheet. As a result,the control of the heat transfer becomes less predictable than it wouldhave been if the exact inner wall thickness had been known. Also thearea of the cross section of the ducts depends of the milling depth.Since alterations of that area will result in correspondingly alteredflow conditions in the duct, this will also affect the effective heattransfer and the possibility of predicting the latter.

Moreover, the requirements on the thermal conductivity of the inner walland the webs may differ substantially. By regenerative cooling of anengine wall structure, by which the cooling medium has a high heatabsorption capacity by the large coolant mass flow and largely consistsof fuel to be used in a subsequent combustion process, the conductivityof the inner wall is much more decisive for the outcome of the coolingthan is the conductivity of the webs. By so called dump cooling, bywhich the cooling medium has a low heat absorption capacity by a lowcoolant mass flow, the heat conductivity of the webs may be moredecisive for the outcome of the cooling than will the conductivity ofthe inner wall. This insight has not been mentioned at all by prior art.

THE OBJECT OF THE INVENTION

The object of the present invention is to provide an engine wallstructure and a method of producing an engine wall structure asinitially defined, by which heat is effectively and predictablytransferred from the inner wall to the outer wall through a coolingmedium, preferably a fuel, in one or more ducts and through the materialof the webs that delimit said duct or ducts and that connect the innerand outer walls.

The invention shall also present an engine wall structure theconstruction of which is such that it promotes the obtaining of a veryprecisely controlled inner wall thickness upon generation of the webs aswell as a facilitated subsequent attachment of the outer wall to thewebs, especially when the inner wall material is different from theouter wall material and not easily connected by any metal fusionprocess. The design of the engine wall structure should also be suchthat it takes into consideration the different heat conductivityrequirements of the inner wall and the webs.

SUMMARY OF THE INVENTION

The object of the present invention is achieved by means of the methodinitially defined, characterised in that the webs are formed byapplication of a first material onto the inner wall, said inner wallbeing comprised by a second material of other composition and other heatconductivity than said first material.

Any suitable technique for applying the webs to the inner wall may beused, such as welding of solid pieces of the first material onto theinner wall. However, deposition of the first material, preferablyelectro-deposition, is preferred.

By building the webs by means of application thereof onto the innerwall, preferably by deposition and most preferably by means ofelectro-deposition, the thickness of that wall will not be affected likewhen the webs are produced through machining of the inner wall, while,at the same time, the height of the web can be very finely adjusted, forexample by means of a final milling of the web top. By using materialsof different composition and heat conductivity, the webs may be tailoredfor their individual, specific functions, especially regarding theconductivity. Subsequent to the formation of the webs, the outer wall isattached to the webs.

Preferably, a removable mask is placed onto said inner wall before thedeposition of the webs is begun, said mask defining spaces in which thewebs are deposited onto the inner wall. Thereby, a precise deposition ofthe web material is promoted.

According to a preferred embodiment the outer wall is connected to thewebs by means of a metal fusion operation, preferably welding, and mostpreferably laser welding. Accordingly, the outer wall comprises a sheetor the like that is connected to the webs.

Preferably, the composition of the material of the webs is substantiallyequal to the composition of the material of the outer wall. Thereby, anymetal fusion process for attaching the second wall to the webs isfacilitated.

Preferably, the material of the inner wall has higher heat conductivitythan the material used for the webs. This is typically an advantage inthose cases when there is a regenerative cooling with a high coolantflow rate or when the cooling medium has a high density, such as when inliquid state, resulting in a high heat absorption, but still arelatively low temperature of the cooling medium and, accordingly, in arelatively low temperature of the webs and the outer wall. The heatconductivity of the material of the inner wall will be decisive for theamount of heat that will be transferred to the cooling medium. The websand the outer wall may then, preferably, be made of a material of highermechanical strength than the material of the inner wall, while theirconductivity is of less importance. Preferably, regenerative cooling isapplied to stage combustion cycle rocket engine nozzles or expandercycle rocket engine nozzles.

In a preferred embodiment, with rapidly flowing cooling medium or acooling medium of high density, preferably liquid fuel, the inner wallcomprises a copper or a copper-based alloy, and the webs comprise steel.Typically, this is preferred for a so-called regenerative cooling whenhydrogen or kerosene to be used as fuel is also used as the coolingmedium. The flow of the cooling medium should be such that a temperaturewell below the melting point of copper or copper alloy is obtained inthe inner wall, preferably below 800 K. The use of a material with aremarkably lower heat conductivity, such as steel, for the inner wall,would result in a build up of a too high temperature in the inner walland, as a result, a deterioration of the inner wall material.

Several materials, such as steel, used for inner walls and webs haverelatively low heat conductivity at low temperatures. A low temperatureof the cooling medium, for instance at the cooling duct inlet, willresult in a low temperature of the engine wall webs, and a low heatconductivity thereof. Also, if the heat transferability of the coolingmedium is poor, for example due to a low flow rate or due to a lowcooling medium density, it would be desired to compensate this by theuse of a highly heat conductive material, such as aluminium, for thewebs, and possibly also for the outer wall. Therefore, according to oneaspect of the invention, the material of the webs has higher heatconductivity than the material of the inner wall. This feature ispreferred for so called dump cooling. Preferably, dump cooling isapplied to gas generator cycle rocket engine nozzles.

If the cooling ability of the engine wall structure, including thecooling medium, is poor due to a low cooling medium flow rate or a lowcooling medium density, the temperature of the inner wall might be tohigh for permitting the use of a highly heat-conducting material such asaluminium for the inner wall. In such cases it is preferred that thetemperature resistance of the material of the inner wall is better thanthat of the web material. Thus, according to a preferred embodiment ofthe invention, the inner wall comprises steel or copper and the webscomprise aluminium or an aluminium-based alloy.

The object of the invention is also obtained by means of an engine wallstructure that comprises an inner wall, to which hot gas is admittedduring engine operation, an outer wall, which is colder than the innerwall during engine operation, and at least two webs that connect theinner wall with the outer wall and delimit a cooling duct between saidwalls, characterised in that the webs are mainly comprised by a firstmaterial and that the inner wall is mainly comprised by a secondmaterial of other composition and other heat conductivity than saidfirst material. Preferred embodiments of the engine wall structure ofthe invention include those embodiments that have been described abovewith regard to the inventive method, especially with regard to thespecific compositions of the first and second materials.

Further features and advantages of the present invention will bedisclosed in the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described byway of example, with reference to the annexed drawings, on which:

FIG. 1 shows a cross section of a nozzle provided with an engine wallstructure according to the invention.

FIG. 2 is an enlargement of a segment of the engine wall structureaccording to FIG. 1.

FIG. 3 is a cross section of an engine wall structure according to afirst embodiment of the invention,

FIG. 4 is a cross section of an engine wall structure according to asecond embodiment of the invention, and

FIG. 5 is a cross section of a part of the engine wall structure duringthe manufacture thereof.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 are schematic representations of the thrust nozzle 1 of arocket engine. The nozzle 1 comprises and is defined by a cone-shaped orbell-shaped engine wall structure 2. The engine wall structure 2 isprovided with an inner wall 3 and an outer wall 4, interconnected by aplurality of webs 5, as shown in FIGS. 3 and 4. In the space between theinner wall 3 and the outer wall 4 there are ducts 6 that are used forcooling purposes. During operation of the engine a cooling medium,preferably the fuel or part of the fuel of the engine, is permitted toflow through the ducts 6 for the purpose of cooling the engine wallstructure 2. This technique applies to satellite launchers and spaceplanes, and also in satellite thrusters, nuclear reactors and highefficiency boilers, and it can also be applied to heat shields or to thenose cones of vehicles travelling at very high speed. When a fuel,preferably in a liquid state, is used as the cooling medium, thetechnique is called regenerative cooling. Then, the heat absorption ofthe cooling medium is relatively high, since a large mass of fuel ispermitted to flow through the engine wall ducts 6. When the coolingmedium consists of a gas or gas mixture that is not further used for anyparticular purpose, but only used for cooling purposes and then exitedinto the atmosphere, the technique is called dump cooling. Then, theheat absorption of the cooling medium is relatively low. Typically, dumpcooling is applied when the flame of the engine generates a relativelylow heat load.

The inner wall 3 and the outer wall 4 are mainly constituted by metals,preferably different metals of different heat conductivity and differentmechanical strength, since the requirements on such properties willdiffer for the inner and outer walls 3, 4. The webs 5 are also made ofmetal.

The cooling ducts 6 are divided by the webs 5 and extend in thelongitudinal direction of the nozzle 1, i.e. in the hot gas flowdirection, as seen in particular in FIG. 2. The nozzle is cone-shaped,whereby the width of the ducts 6 increase towards the wider end of thenozzle 1, and the thickness of the webs 5 is generally constantthroughout the length of the nozzle 1.

FIG. 3 shows a first embodiment of the invention in which the inner wall3 is mainly constituted by a material of different composition anddifferent heat conductivity than the material of the webs 5 directlyconnected thereto. The webs 5 have been attached to the inner wall 3 bymeans of a metal deposition method, preferably electro-deposition. Thedeposition or build up of the webs is schematically represented in FIG.5, in which there is shown a mask 7 that is placed on top of the innerwall 3 before the application of the webs. The mask 7 has a height orthickness in a direction normal to the surface of the inner wall 3 thatcorresponds to or even exceeds that desired height of the webs 5. Themask 7 leaves open channels 8 into which the web material is brought forthe purpose of being deposited on the inner wall 3. Once the depositionof the web material has been ended, the mask 7 is removed from thesurface of the inner wall 3.

The mask 7 may be tailored in accordance with different pre-conditions,thereby greatly facilitating the application of different webgeometries. FIG. 4 shows an embodiment in which the mask 7 has beengiven such a shape that the resulting webs 5 get wider towards the outerwall 4. This specific geometry might be used in order to diminish thecross section area of the ducts 6 in order to enforce a more rapid flowrate of the cooling medium and, thereby, a more effective cooling. Thiseffect is also achieved thanks to the interface area between the websand the outer wall 4 becoming larger than would otherwise be the case.

Once the deposition of the web material has been completed, the heightof the webs 5 is finely adjusted, for example by means of milling, inorder to establish a very precise web height, and, possibly, also theweb width. Preferably, but not necessarily, this operation is performedafter removal of the mask 7. Thereafter, the outer wall 4, constitutedby a sheet of material, is positioned on top of the webs 5 and attachedthereto, preferably by means of any metal fusion operation, such aslaser welding.

As already told, the web material differs from the inner wall material,in particular regarding its heat conductivity, and possibly also withregard to its mechanical strength and temperature resistance.

The outer wall material and the web material should be easilyinterconnected by means of any metal fusion process. This is most easilyachieved if their compositions are substantially equal. Accordingly, theouter wall material and the web material may have corresponding heatconductivity properties as well as mechanical properties.

For applications with a high cooling effect of the cooling medium, forexample when the flow rate of the latter is high and/or when the densitythereof is high, as for a liquid cooling medium, the heat conductivityof the inner wall 3 will be crucial to the total heat transfer. Then, ahigh conductivity material such as copper is preferred as the inner wallmaterial. The web material as well as the outer wall material should, ofcourse, also have a certain conductivity, but since a large part of theheat is absorbed and carried away by the cooling medium, it might besubstantially lower than that of the inner wall 3. Therefore, a materialof higher mechanical strength could be used as web material and outerwall material. In a preferred embodiment steel is preferred as web andouter wall material.

For applications with a low cooling effect of the cooling medium, forexample when the flow rate of the latter is low or when the densitythereof is low, as for a gaseous cooling medium, the heat conductivityof the webs becomes increasingly important in order to let a larger partof the heat be transferred from the inner wall 3 to the outer wall 4through the webs. It is then preferred that the heat conductivity of theweb material is higher than that of the inner wall material. Accordingto a preferred embodiment, the inner wall material mainly comprisessteel, while the web material mainly comprises aluminium or an aluminiumalloy. This is a preferred embodiment in cases when the cooling mediumin the ducts 6 has a relatively low temperature, thereby permittingsteel to be used as the inner wall material, and when the cooling mediumis in gaseous state with inherently poor heat absorption capacity.

It should be realised that the above description of the invention onlyhas been made by way of example and that, of course, a person skilled inthe art will recognise a plurality of alternative embodiments, allhowever within the scope of the invention as defined in the annexedpatent claims, supported by the description and the drawings.

1. A method of producing an engine wall structure that comprises aninner wall, to which hot gas is admitted during engine operation, anouter wall which is colder than the inner wall during engine operation,and at least two webs that connect the inner wall with the outer walland delimit a cooling duct between the walls, comprising forming thewebs by application of a first material onto the inner wall, the innerwall being composed by a second material of other composition and otherheat conductivity than the first material.
 2. A method according toclaim 1, wherein, subsequent to the formation of the webs, the outerwall is attached to the webs.
 3. A method according to claim 1, whereinthe webs are formed by deposition of the first material onto the innerwall.
 4. A method according to claim 3, wherein a mask is placed ontothe inner wall before the deposition of the webs is begun, the maskdefining spaces in which the web material deposited onto the inner wall.5. A method according to claim 1, wherein the outer wall is connected tothe webs by means of a metal fusion operation.
 6. A method according toclaim 5, wherein the metal fusion operation is a welding operation.
 7. Amethod according claim 1, wherein the composition of the material of thewebs is substantially equal to the composition of the material of theouter wall.
 8. A method according to claim 1, wherein the material ofthe inner wall has higher heat conductivity than the material used forthe webs.
 9. A method according to claim 1, wherein the inner wallcomprises a copper or a copper-based alloy, and the webs comprise steel.10. A method according to claim 1, wherein the material of the innerwall has a higher temperature resistance than the material of the webs.11. A method according to claim 1, wherein the material of the webs hashigher heat conductivity than the material of the inner wall.
 12. Amethod according to claim 11, wherein the inner wall comprises steel andthe webs comprise aluminum or an aluminum-based alloy.
 13. A methodaccording to claim 1, wherein the material of the outer wall and thematerial of the webs have corresponding heat conductivity properties.14. A method according to claim 1, wherein the material of the outerwall and the material of the webs have corresponding properties as totheir mechanical strength.
 15. A method according to claim 1, wherein aheight of the webs is adjusted by a machining operation before the outerwall is attached thereto.
 16. An engine wall structure that comprises aninner wall, to which hot gas is admitted during engine operation, anouter wall, which is colder than the inner wall during engine operation,and at least two webs that connect the inner wall with the outer walland delimit a cooling duct between the walls, wherein the webs aremainly comprised by a first material and that the inner wall is mainlycomprised by a second material of other composition and other heatconductivity than the first material.
 17. An engine wall structureaccording to claim 16, wherein the composition of the material of thewebs is substantially equal to the composition of the material of theouter wall.
 18. An engine wall structure according to claim 16, whereinthe material of the inner wall has higher heat conductivity than thematerial used for the webs.
 19. An engine wall structure according toclaim 16, wherein the inner wall comprises a copper or a copper-basedalloy, and that the webs comprises steel.
 20. An engine wall structureaccording to claim 16, wherein the material of the inner wall has ahigher temperature resistance than the material of the webs.
 21. Anengine wall structure according to claim 16, wherein the material of thewebs has higher heat conductivity than the material of the inner wall.22. An engine wall structure according to claim 21, wherein the innerwall comprises steel and that the webs comprises aluminum or analuminum-based alloy.
 23. An engine wall structure according to claim16, wherein the material of the outer wall and the material of the webshave corresponding heat conductivity properties.
 24. An engine wallstructure according to claim 16, wherein the material of the outer walland the material of the webs have corresponding properties as to theirmechanical strength.
 25. An engine wall structure according to claim 16,wherein the engine wall structure defines a thrust nozzle wall of arocket engine.